This proposal will continue work begun in this laboratory, on an effective intra-aortic balloon pump (IABP) for infants. Miniature balloons and a drive system have been constructed and proven effective in heart failure in 3 to 8 Kg animals. We propose to continue animal experimentation to precisely define the most effective size balloons for a wide range of patient sizes and conditions. It is recognized that after surgical correction of a congential defect, IABP may be effective to support the circulation in the early postoperative phase. We propose to continue animal experimentation to develop other criteria for the use of IABP and to define in which congenital defects IABP is effective and in which is not suitable. We believe effective support may be extended to situations not presently suited for IABP by changing the position of the balloon or by changing the pumping phase of the balloon. We propose to establish a method to determine the intra-aortic pressure and the effect of the balloon pumping by measuring the pressure waves of the driving gas to the balloon, much the same way as we do it for our aritifical hearts. This will eliminate the need for additional open pressure lines in the baby.